U.S. patent application number 12/709948 was filed with the patent office on 2011-02-10 for downhole device.
Invention is credited to Andrew Jenner.
Application Number | 20110030973 12/709948 |
Document ID | / |
Family ID | 41129936 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110030973 |
Kind Code |
A1 |
Jenner; Andrew |
February 10, 2011 |
Downhole Device
Abstract
A stop collar or like device is formed in one piece to have a
portion for a tool to be attached. Movement of the tool allows the
collar to be drawn tightly into engagement onto a pipe or other
tubular member. A bow centraliser has alternate bows longitudinally
offset to reduce initial insertion force. The centraliser may be
formed to have end bands of the type used in the stop collar.
Inventors: |
Jenner; Andrew; (Vechta,
DE) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD, P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Family ID: |
41129936 |
Appl. No.: |
12/709948 |
Filed: |
February 22, 2010 |
Current U.S.
Class: |
166/382 ;
166/241.1 |
Current CPC
Class: |
E21B 17/1028 20130101;
E21B 37/02 20130101 |
Class at
Publication: |
166/382 ;
166/241.1 |
International
Class: |
E21B 23/00 20060101
E21B023/00; E21B 17/10 20060101 E21B017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2009 |
GB |
0913979.1 |
Claims
1. A one-piece device for engagement over and onto a downhole
tubular, the device comprising a generally cylindrical band having
at least one arcuate portion with opposing end regions, the end
regions being coupled together by a connecting portion having a
pair of arm portions extending on respective sides of a body
portion, distal ends of the arm portions extending into the end
regions, the body portion having a formation for engagement therein
of a tool whereby rotation of the body portion by a tool varies the
size of the device, the device further comprising engagement means
to secure the arm portions with respect to an adjacent end region
so that the device can be locked.
2. The device of claim 1, having a plurality of arcuate portions
each having respective end regions, and a corresponding plurality
of connecting portions.
3. The device of claim 1, wherein the connecting portions are
generally S shaped.
4. The device of claim 1, wherein the or each arcuate portion has
prolongations to form guides for constraining sideways movement of
the arm portions.
5. The device of claim 4, wherein the guides have teeth to interact
with counterpart teeth on the arm portions to form the engagement
means.
6. The device of claim 1, wherein the device is be substantially
circular with an axis, the or each arcuate portion have a first
axis-parallel width and the arm portions have a second
axis-parallel width that is less than the first width.
7. The device of claim 1, being formed of micro-alloy steel.
8. A stop collar or like device which is adapted to mount around a
tubular member such as a length of pipe, drill string or tubing
string to grip the exterior of the tubular member and restrict
axial travel of any further associated product that is assembled
onto the exterior of the tubular member along the member, the
device being characterised in that the construction of the stop
collar and a means of activating radial gripping of a tubular
member is from a single piece of material.
9. A method of securing a one-piece stop collar to a tubular
comprising sliding the stop collar over the tubular to a desired
location, and rotating a portion of the stop collar to draw the
collar tighter onto the tubular.
10. A centralizer having first and second opposing end collars, the
end collars being axially separated by plural spring bows, the
spring bows forming a generally convex curve, with first bows
extending from the first end collar substantially axis-parallel for
a first distance before extending via the curve into the second end
collar, and second bows extending curvedly from the first end
collar and into a substantially axis-parallel portion at the second
end collar, whereby the centralizer is formed of a single
piece.
11. A centralizer according to claim 10, comprising the device of
claim 1.
Description
RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn.119
or 365 to Great Britain, Application No. 0913979.1, filed Aug. 10,
2009. The entire teachings of the above application are
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to the field of downhole
devices, and more specifically but not exclusively to the field of
such devices usable in oil and/or gas extraction. Some embodiments
concern stop collars or like devices. Some others relate to
centralizers.
BACKGROUND
[0003] Stop collars are used in downhole environments, for instance
in the oil and gas industry, to mount around a tubular member such
as a length of pipe, drill string or tubing string to engage and
grip the exterior of the tubular member. Stop collars provide a
stop shoulder on the tubular member to restrict axial travel along
the tubular member of any further associated product--for example a
centralizer--that is assembled onto the exterior of the tubular
member.
[0004] As known to those skilled in the art, a stop collar,
sometimes referred to as a stop ring or similar terminology, is
commonly used to restrain the axial movement of products such as
but not limited to centralizers that are assembled onto the tubular
members (sometimes referred to as "tubulars") of a well casing.
[0005] Centralizers are devices that engage over a tubular member,
as above, and that have an external envelope intended to contact
the bore to maintain that tubular member generally out of contact
within--and ideally central within--the bore.
[0006] Stop collar design must cope with free fitment onto tubulars
having poorly toleranced outer diameters. The reader is directed to
American Petroleum Institute API 5CT which states that the tubular
outer diameter tolerance is "nominal diameter+1%". It may be seen
that a most common tubular size of "nine and five-eights" (95/8
inch, 24.47 cm) could be 9.625 inch to 9.721 inch (24.47 cm to
26.92 cm) outer diameter. Any design applied must take up this
tolerance as pre-requisite to applying sufficient load to give the
desired axial load restraint.
[0007] The many current stop collars or like devices used to resist
axial loading rely on various methods of partially penetrating into
the surface of the tubulars under action of locally applied axial
loads. Two of the most common methods employed are toughened steel
screws radially dispersed around the circumference of the stop
collar, and hardened steel inserts wedged between the stop collar
and the tubular surface.
[0008] Penetration of the surface of the tubulars creates
significant marking which can lead to stress concentration and
cause stress corrosion cracking when the tubular is placed in its
operating environment. Where tubulars consist of an alloy
containing for example chrome, commonly 13% or more, galvanic
corrosion between the toughened steel screws and the chrome alloy
surface exacerbates the tubular life failure rate.
[0009] Current arrangements are unable to resist axial loads of a
magnitude similar to the load bearing capabilities of the
associated components they are supposed to hold in position i.e.
centralizers in either tension or compression. Increasing the
number of radially disposed screws or wedges dramatically increases
the stress corrosion potential. Users seek to balance between
desired axial holding ability and the said increase in stress
corrosion.
[0010] It is a further problem that assembly of the stop collar
onto the tubular, in the field, is frequently delegated to
unskilled labour. It is common practice to assemble, for example
screws, with little regard to correct torques applied or to whether
the threads are suitably lubricated. This latter point has an
inbuilt hazard in that screws are frequently split, through
incorrect torque applied, which will not be apparent to the
personnel carrying out the assembly. The result possibly leads to
even lesser axial holding ability as the tubular is traversed into
its operating position. By default the screws employed must be
small enough to fit with suitable clearance within the annulus
formed between the tubular on which they are affixed and the
wellbore or internal diameter of previously installed larger
tubular, said screws commonly being 1.27 cm.times.1.27 cm
(1/2''.times.1/2'') long socket set screws which have only a 0.635
cm (1/4'') across flats hexagonal drive form. Hexagonal wrenches
are small, have a very short life and the tendency is not to change
for new hexagonal drives before rotational failure of the hexagonal
drive corners, with resultant insufficient torque input to achieve
desired axial holding forces.
[0011] The protrusion of screws or wedge devices beyond the outer
diameter of the stop collar main body considerably restricts the
use of traditional stop collars in a narrow annulus configuration
existing between the tubular to which the stop collars are affixed
and the wellbore or internal diameter of a previously installed
larger tubular.
[0012] The aforementioned design practices of multiple part stop
collar constructions may result in lost parts of the stop collar,
or associated components, falling into the wellbore. This is
considered as catastrophic in the industry.
[0013] Problems also occur with centralizers where the bore has an
upper part of a generally smaller cross section than a lower part
where the centralizer is needed to act. Clearly the centralizer
must pass through the upper part without breakage, and without
requiring too great an insertion force. The two constraints may of
course be interrelated.
[0014] One such scenario is with so-called "under-reamed" bores.
This occurs for example where wellbores are `opened out` in a
region lower than a previously installed tubular.
[0015] In one example, a drill bit is passed through the 21.68 cm
(8.535'') internal diameter. of a previously installed 24.45 cm
(95/8'') tubular and then the bit is rotated out of concentric to
create a 24.13 cm (9.5'') hole. So, a centralizer is required to
fit the nominal size of 24.13 cm (9.5'') diameter so as to
centralize a tubular in that bore, but also is required to pass
through 21.58 cm (8.535'') diameter of the upper tubular.
SUMMARY
[0016] In a first aspect there is provided a one-piece device for
engagement over and onto a downhole tubular comprising a generally
cylindrical band having at least one arcuate portion with opposing
end regions, the end regions being coupled together by a connecting
portion having a pair of arm portions extending on respective sides
of a body portion, distal ends of the arm portions extending into
the end regions, the body portion having a formation for engagement
therein of a tool whereby rotation of the body portion by a tool
varies the size of the device, the device further comprising
engagement means to secure the arm portions with respect to an
adjacent end region so that the device can be locked.
[0017] The device may have a plurality of arcuate portions each
having respective end regions, and a corresponding plurality of
connecting portions.
[0018] The connecting portions may be generally S-shaped.
[0019] The arcuate portions may have prolongations to form guides
for constraining sideways movement of the arm portions.
[0020] The guides may have teeth to interact with counterpart teeth
on the arm portions to form the engagement means.
[0021] The device may be substantially circular with an axis, the
or each arcuate portion have a first axis-parallel width and the
arm portions have a second axis-parallel width that is less than
the first width.
[0022] The device may be of a micro-alloy steel. An example that
may be used is boron steel.
[0023] In a second aspect, there is provided a stop collar or like
device which is adapted to mount around a tubular member such as a
length of pipe, drill string or tubing string to grip the exterior
of the tubular member and restrict axial travel of any further
associated product that is assembled onto the exterior of the
tubular member along the member, the device being characterised in
that the construction of the stop collar and a means of activating
radial gripping of a tubular member is from a single piece of
material.
[0024] In a third aspect there is provided a method of securing a
one-piece stop collar to a tubular comprising sliding the stop
collar over the tubular to a desired location, and rotating a
portion of the stop collar to draw the collar tighter onto the
tubular.
[0025] Prior art examples, where sufficient annular width allows,
have attempted to draw the open ends of a stop collar band or ring
together for example with bolt and nut designs. The desire to
change developed circumferential length requires that slippage
takes place between all of the internal diameter of the stop collar
and the surface of the tubular to which it is being affixed yet
achieve high radial loads. It is given that the two desires are
contradictory.
[0026] In a fourth aspect, a centralizer has first and second
opposing end collars that are axially separated by plural spring
bows, the spring bows forming a generally convex curve, with first
bows extending from the first end collar substantially axis
parallel for a first distance before extending via the curve into
the second end collar, and second bows extending curvedly from the
first end collar and into a substantially axis parallel portion at
the second end collar, whereby the centralizer is formed of a
single piece of material.
[0027] The material may be a micro-alloy steel. The micro-alloy
steel may be boron steel.
[0028] One or both collars of the centralizer may be in accordance
with the first aspect.
[0029] In a further aspect there is provided a device for
disposition on a tubular member, the device having a band or
collar, and having plural resilient axial protrusions for
distributing point loading.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Example embodiments will now be described with reference to
the attached drawings to enable the reader to better understand the
invention. In the drawings:
[0031] FIG. 1 shows schematically a typical arrangement of a
tubular centralized within a borehole.
[0032] FIG. 2 is a perspective view of a stop collar of a first
embodiment.
[0033] FIG. 3 is a perspective view of a stop collar of a second
embodiment.
[0034] FIG. 4 is a perspective view of a first embodiment of a
centralizer;
[0035] FIG. 5 shows an exemplary blank that may be used in forming
the centralizer of FIG. 4.
[0036] FIG. 6 shows a graph of insertion force for a centralizer
embodying the invention by comparison with a prior art
centralizer.
[0037] FIG. 7 shows a second embodiment of a centralizer,
[0038] FIG. 8 shows a cut-away view of a part of the centralizer of
FIG. 7.
[0039] FIGS. 9 to 20 show further embodiments of centralizers.
[0040] FIG. 21 shows bow an embodiment of an offset bow centraliser
has a less savage insertion force requirement than a conventional
bow centraliser.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Referring to FIG. 1, a tubular is formed from a plurality of
lengths 110 connected together by couplings 111. As is well known,
a centralizer 113 is supported on each length 110 by way of a
respective stop collar 112. Each centralizer 113 is arranged to
support the tubular, formed of the lengths 10, within the borehole
114 such that the tubular is substantially centrally arranged.
[0042] Referring to FIG. 2, an embodiment of a stop collar 1 is a
broad generally cylindrical band formed of a single piece of
material. The collar 1 has three arcuate portions 10, 20, 30 which
have respective opposing end regions 10a, 10b; 20a, 20b; 30a, 30b.
The end regions 10a, 10b; 20a, 20b; 30a, 30b are coupled together
by respective connecting portions 40, 50 60. Each connecting
portion 40, 50, 60 has a respective pair of narrow arm portions
41,42; 51,52; 61,62 extending on respective sides of a generally
circular body portion 45; 55; 65. The connecting portions 40, 50,
60 with their arm portions 41,42; 51,52; 61,62 describe a generally
"S" shape in the shown configuration, and the end regions 10a, 10b;
20a, 20b; 30a, 30b generally conform to the external form of the
connecting portions 40, 50, 60.
[0043] Other shapes are possible, of course, for example "Z"
shapes.
[0044] The arm portion 42 extends from a downwardly (as shown)
inset location 43 of the end region 20a of the second arcuate
portion 20, and extends--in this configuration--parallel to the
upper circumference 2 of the collar 1. The end region 11b of the
first arcuate portion 10 extends into a prolongation 11 forming a
circumferential finger 11. The finger 11 serves at least partly to
constrain the adjacent arm portion 42 to prevent sideways movement
and consequent distortion of the collar 1.
[0045] Engagement means is provided to allow the collar 1 to be
locked. In this embodiment the finger 11 has a lower (as shown)
surface 11a abutting an upper (as shown) surface 42a of the arm
portion 42. The finger 11 has toothed projections 12 on the lower
surface 11a and the arm portion 42 has toothed projections 44 on
the upper surface 42a to form the engagement means by securing the
finger 11 to the arm portion 42. A like arrangement is provided at
each arm portion 41, 42; 51,52; 61,62.
[0046] The circular body portions 45, 55, 65 have a formation for a
tool. In this embodiment, the formation is a hex hole 70
dimensioned to be engaged by a hex key.
[0047] In use, the stop collar 1 is fitted and secured to a tubular
by sliding the stop collar 1 over the tubular to a desired
location, and rotating the body portions 45,55,65 one-by-one to
draw the collar into tight engagement onto the tubular. The
engagement state is maintained by the interlocking of the teeth of
the toothed projections in a sort of ratchet fashion.
[0048] In summary, there is provided a circular band with
radially-disposed cut forms each capable of being distorted or
moved to draw adjoining areas closer together to change in total
the circumferential developed-length of the stop collar in
sequential minor increments to accommodate take up of the tubular
diametral tolerance. Following this additional intentional
distortion or movement gives rise to a radially inwards loading the
sum of which supplies sufficient contact force between the inner
diameter of the stop collar and the tubular to which it is affixed,
to maintain it secured. The number of cut forms is not critical to
the invention. In different embodiments different numbers than
three may be provided commensurate with the tubular base diameter,
the degree of tubular manufacturing tolerance to be taken up and
the level of required axial holding ability of the final
assembly.
[0049] In addition to addressing the problems of the prior art
designs of stop collar as discussed above, embodiments provide a
capability of accommodating for variations in diameter which exist
on the tubular member due to manufacturing tolerances of tubulars.
The segmental cut form design of the present invention may locally
distort at each segment to proportionally reduce or eliminate
contradictory radial and circumferential loads.
[0050] Distortion or movement together of segmental forms may be
activated for example but not limited to substantially enlarged
hexagonal wrenches for example 12 mm across flats as opposed to the
prior art forms of common set screws with 6 mm across flats
hexagonal drive apertures. Failure of the wrenches other than for
reasonable wear is improbable.
[0051] In an embodiment the material chosen for the stop collar is
heat-treatable to improve, for example, shear and tensile section
strength properties. Such heat-treated strength may be of the order
90 tons per square in.
[0052] Segmental cut forms may be varied at will to suit design,
manufacture, field assembly or performance demands.
[0053] The product may be manufactured to an undersize internal
diameter to the tubular diameter for which it is intended to fit.
Then the radially-disposed cut forms may be segmentally opened in
reverse direction to expand the stop collar for easy assembly onto
the tubular
[0054] Internal diameter of the stop collar may be coated, deformed
or machined to give for example low stress bearing point(s) to
create a desirable friction increase between the modified stop
collar internal diameter and surface of the tubular member to which
it is affixed.
[0055] Where galvanic or stress corrosion conditions are to be
avoided, the internal diameter of, say, a steel stop collar or ring
main body may be coated with a suitable interface material to
negate these problems. Example coatings may be, but not limited to,
zinc or aluminium.
[0056] Unlike prior art designs, that of the embodiment enables the
stop collar to closely hug the external diameter of the tubular to
which it is affixed and:--
[0057] have a flush external diameter thereby removing external
protrusions which may interfere with free passage through the
wellbore,
[0058] facilitate use in narrow annulus configuration between the
tubular member and the wellbore or previously installed larger
tubular member
[0059] plus, minimise encroachment of fluid flow cross sectional
area of the annulus so formed.
[0060] FIG. 3 shows a second embodiment in which the hex hole is
supplanted by a different formation--here three smaller holes 80,
aligned in a row. Other formations will be readily conceived by the
skilled person.
[0061] Although the technique of the invention is shown in use as a
stop collar, it is also applicable to other components used in
similar context.
[0062] Referring to FIG. 4, a one-piece centralizer 200 has first
and second opposing end collars 210,220 that are axially separated
by plural spring bows 240-245. Each spring bow forming a generally
convex curve. First bows 241,243,254 extending from the first end
collar 210 with a respective portion 241a, 243a, 245a substantially
axis parallel for a first distance before extending into a
continuously curved portion 241b, 243b, 245b to the second end
collar 220. Second bows 240,242,244 extend through respective
curved portions 240b, 242b, 244b from the first end collar 210 and
into a substantially axis parallel portion 240a, 242a, 244a at the
second end collar 220. In this embodiment, the end collars are
plain, and the centralizer be formed for cooperation with a stop
collar.
[0063] However, in other embodiments--see for example FIGS. 7 and
8, the end collars are each end collar is formed similarly to the
collar of FIG. 2.
[0064] In the illustrated embodiment there are 6 bows separated
into two sets of three, with--in a circumferential direction--a
first bow-type followed by a second bow-type followed by a first
bow-type. The effect is to reduce very substantially (around 45%)
the initial insertion force into a diameter that is smaller than
the free outside diameter over the bows.
[0065] The centralizer of the described embodiment has bows of
equal length, and this means it can be made from a single blank, an
example of which is shown in FIG. 5.
[0066] Referring to FIG. 5, a blank 300, is formed from a single
sheet of boron steel. The blank has two transverse web portions
302, 303 spaced apart by six spaced longitudinal web portions 304
which extend substantially parallel to one another and
perpendicular to the webs 302,303. The first and second transverse
web portions 302, 303 are generally rectangular in shape, are
mutually parallel. The six longitudinal web portions 304 extend
between the transverse web portions 302,303 to define therebetween
five apertures 309 of equal size. The outer longitudinal web
portions 304 are inset from the ends of the transverse web portions
by around half the width of the apertures 309 to leave free end
portions 310,311 of the transverse web portions. The free end
portions are, in a first embodiment of a centralizer, overlappingly
secured together so that each first end portion 310 overlaps its
corresponding second end portion 311 whereby the centralizer forms
a generally cylindrical device. In other embodiments, the length of
the free end portions is greater, and in these embodiments the free
end portions are subsequently formed into connecting devices.
[0067] The web portions 302,303 form the collars 210, 220 of FIG.
4. The longitudinal web portions 304 form the bows 240-245 of FIG.
4. Bending operations are performed on the bows to achieve the
configuration of FIG. 4.
[0068] It will, of course, be understood that this is a purely
exemplary blank and is used here illustratively. Boron steel is
only one example of the materials that may be used, which include
mild steel and many other different materials. One class of
steel--which includes boron steel--is the class of micro-alloy
steels. This class has been shown to be generally useful.
[0069] The blank is formed by cutting or punching from the sheet. A
preferred technique is a high accuracy computer-controllable
cutting method such as laser-cutting or water jet-cutting. Such a
technique can allow great flexibility, for instance enabling
`specials` to be produced without a need for expensive dedicated
tooling.
[0070] The blank is then cold-formed into a generally cylindrical
shape. This may be accomplished by rolling or by other techniques
known in themselves in the art.
[0071] The relatively ductile nature of the boron steel material
forming the blank allows for the blank to remain in its cylindrical
state after the forming has taken place.
[0072] With a known one-piece centralizer a major benefit is that
due to the efficiency of leaf spring bows blending homogenously
into the end bands at either end, the centralizer could be slide
fit into the nominal size wellbore diameter as they were onto the
load/deflection performance curve immediately upon the onset of
load. By contrast, the traditional spring bow products needed to be
greatly oversize to achieve performance and so imparted a high
initial insertion force.
[0073] Referring to FIG. 6, the full (undashed) line shows a
centralizer to exactly the same bow chordal width and bow height
and without longitudinal offset of every other bow.
[0074] On this type the initial insertion force is quite savage as
all 6 bows are being urged together towards the restriction and the
centralizer is trying to change the developed length so as to
conform to the restriction. Typically there is a loss of bow height
by as much as 1.5 cm (0.6 in) on diameter as permanent set or yield
occurs where the bow meets the end band. This loss means the
centralizer outside diameter can reduce to 23.5 cm (9.25'') to
locate in a 25.1 cm (9.875'') well bore. This itself is an
improvement over previous types of centralizer.
[0075] The dashed curve shows the performance of a 6-bow
centralizer embodying the invention where we still have the
contradiction of pushing towards the resistance which is against
bows trying to change their developed length. With only 3 bows
entering initially the initial insertion force is only 60%, (there
is still some reshaping of the bow profile until it conforms to the
restriction diameter). However it remains within the specified
yield and on test only lost about 0.4 mm (0.017'') on bow
height--as well as considerably lower insertion force and some 25%
reduction on re-start of axial travel within the restriction we now
have a near 25.1 cm (9.875'') outside diameter centralizer for the
25.1 cm (97/8'') well bore.
[0076] This is more clearly described later herein with respect to
FIG. 21.
[0077] It may also be noted on the dashed curve that the 1st set of
3 bows entering takes approximately 5956N (1339 lbf) whereas the
2nd set of 3 only takes approximately 3816 N (858 lbf) to enter.
This is because as the 1st set is being squeezed down in diameter
they are being resisted by the as-yet to enter 2nd set which is, in
effect, being demanded to start changing length before entering the
restriction.
[0078] In FIG. 7, a second centralizer 700 has a pair of end
collars 701, 702, each with formations 705 similar to those
described with reference to FIG. 2. The bows 710 of centralizer 700
are similar to those described with reference to FIG. 4. The end
collars 701, 702 each have flexible protrusions 720 at their outer
ends. The form of these protrusions may be selected as desired.
[0079] In this example--shown more clearly in FIG. 8--the flexible
protrusions 720 axially from each end collar and have a 7' section.
Each of these is apt to flex to distribute point loading forces as
adjacent 7' springs come in contact when the centralizer abuts
against a stopping device placed externally to the centralizer 700
on a tubular.
[0080] In FIG. 9 stop collars 901, 902 are fitted on both sides of
the bow centralizer 903. Each of the stop collars has a
circumferentially distributed plurality of T-shaped projections
904, 905 that extend into corresponding female T-shaped apertures
906, 907 of the centralizer 903. The female apertures 906, 907 have
sufficient clearance to allow for increase in developed length of
the centralizer when the bows are reduced in outer diameter.
[0081] The fixing devices for the stop collars 901, 902 may be
conventional--e.g. set-screws as is commonly provided in existing
products--or may alternatively use the ratchet device described
above with respect to FIG. 2.
[0082] Turning now to FIG. 10, in this figure there will be seen
two stop collars 1001, 1002 and a centralizer 1003. The stop
collars each have half-thickness bayonet fastenings 1004 projecting
parallel with the axis of the centralizer and stop collars. The
bayonet fastenings have outer faces machined to half thickness and
the end bands of the centralizer 1003 are machines to half
thickness on their inner face to allow for engagement by the
bayonets.
[0083] Referring to FIG. 11, in this embodiment there are two stop
collars 1101, 1102 with generally similar bayonet fastenings 1104
to those of FIG. 10, but in this case the centralizer 1103 is
pre-assembled with the stop collars 1101, 1102 so as to be slid on
to a tubular in a single assembly.
[0084] Turning to FIG. 12 two stop collars, 1201, 1202 engage with
a bow centralizer 1203. The stop collars have extending bayonet
fastenings 1204 but the fastenings are engaged with heads 1205 into
apertures 1206. The apertures 1206 are windows that are
sufficiently oversized with respect to the head 1205 of the bayonet
fastening 1204 to allow for the required extension of the bows when
compressed sideways.
[0085] Turning to FIG. 13 there is shown an arrangement with two
stop collars 1301, 1302 and a bow centralizer 1303 on a tubular
1300. The centralizer 1303 has axially outwardly projecting
T-shaped portions 1304 that extend to and engage in suitably-formed
cut-out windows 1305 in the stop rings 1301, 1302.
[0086] Turning to FIG. 14, in this embodiment there are two stop
rings 1401, 1402 and a centralizer 1403 that has axial projections
of the bayonet type 1404, 1405 that engage with the outer
peripheral circumference 1401a, 1402a of the stop collars 1401,
1402.
[0087] Turning to FIG. 15 this is generally similar to FIG. 11 but
in this case the pre-assembled configuration is maintained by
projections 1505, 1506 extending from a centralizer 1503 to the
outer periphery of the stop collars 1501, 1502.
[0088] In FIG. 16, projections 1605, 1606 extend from the
centralizer 1604 into windows 1607, 1608 in the stop collars 1601,
1602.
[0089] FIG. 17 shows an alternative embodiment in which a
centralizer 1701 is freely positioned onto a pipe 1702, in other
words is not constrained by stop collars. Pads 1703, 1704 are
secured to the pipe 1700 both above and below the centralizer and
these allow sufficient clearance to allow for change in the
developed length of the centralizer when the bows 1710 are flexed.
Pads are existing technology and are commonly cast-on composite
materials applied after the centralizer 1701 has been positioned to
the desired axial position upon the pipe/tubular 1700. In this
situation the pipe may rotate freely with respect to the
centralizer which would be prevented from movement itself by
contact against a bore hole wall.
[0090] In FIG. 18 an arrangement somewhat similar to that of FIG.
17 is shown. However in this case the pads 1806, 1807 are secured
to the pipe 1800 and the pads extend into clearance windows 1804,
1805 in the end bands 1802, 1803 of the centralizer 1801. In this
arrangement it is not intended that the pipe should be rotated
since it would scour off the pads if it did so or alternatively
could jam to the centralizer if the centralizer rode over the pads.
In this arrangement it is useful if the pad thickness is similar to
or slightly higher than the centralizer to facilitate passage into
the borehole where annular clearance between the pipe and the
borehole is only slight with the centralizer bows fully compressed
on outer diameter.
[0091] In FIG. 19 a similar arrangement of FIG. 18 is shown. The
pads 1909, 1910 are commonly of composite material cast on to the
pipe 1900. Positioning is usually a hand operation and misalignment
can be present. The material that constitutes the pads is filled
with a particulate matter to improve wear. However this increases
brittleness with a resultant weakness to point loading on
relatively thin pad thicknesses. To overcome this, the
spring-treated centralizer 1901 is formed to have small free-end
leaf springs 1911, 1912 when the clearance aperture-windows
1906,1907 are formed. This allows for the spreading out and evening
of point of contacts.
[0092] FIG. 20 has pads 2010-2011 encased within a metallic cage
that is filled with composite material as it is cast onto the pipe
2000. The cage engages into windows 2002, 2003 of the centralizer
2004. The contact edges under axial load are then metal-to-metal.
This avoids the current weakness of point loading of pure composite
pads. In such a design it is possible to relieve the underside of
the metal cage and create various apertures through the top surface
to maximize composite body thickness.
[0093] FIG. 21 gives a diagrammatic indication of how the bows of
an embodiment of a centraliser 2101 ease the transition of the
centraliser into the restriction 2102 of the bore. Of the
centraliser 2101, shown in partial section, two offset bows 2105,
2107 can be seen. Other bows are not shown for ease of
description.
[0094] It can clearly be seen that as the centraliser 2010 moves
downwardly in the direction shown by the arrow, the first bow 2105
is compressed into the restriction 2102 before the second bow 2107
starts to become compressed by interaction with the restriction
2102.
[0095] This specific embodiment is designed so that one bow is
fully compressed before the other starts to compress. How this is
achieved will be clear to the skilled person, bearing in mind the
relevant diameters and lengths. However the invention is not
restricted to this arrangement and a greater offset may be provided
or a lesser offset may be provided in different embodiments
according to the needs of the application to which the centraliser
is put.
[0096] By contrast, with no offset, all bows will engage at the
same time, and all will need to be compressed during a relatively
small insertion distance, creating a more savage insertion
force.
[0097] While some embodiments of the present invention have been
described using specific terms, such description is for the purpose
of only illustrating the principle and applications of the present
invention, and it is to be understood that modifications or changes
and variations in arrangement may be further made without departing
from the spirit or scope of the appended claims underlying the
technical ideas of the present invention.
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